Studies by this investigator have documented the existence in rat embryos of cell populations--located in intestinal mesnchyme and in several cranial sensory and dorsal root ganglia--which transiently express aspects of the catecholamine (CA) phenotype (1-16). Cells in developing gut, e.g., possess tyrosine hydroxylase (T-OH), dopamine B-hydroxylase, CA fluorescence, and a specific, high-affinity uptake process for CA's. In addition, they respond to elevated maternal glucocorticoid hormones with increased levels of T-OH and a prolonged expression of CA traits. Utilizing these transiently CA populations, the investigator will study factors which control the maintenance (or loss) or neurotransmitter phenotypic expression. Specifically, the plan is to 1) investigate the site of glucocorticoid action on gut cells; 2) determine the fate of transiently CA cells in gut by pharmocological prolongation of CA traits and simultaneous detection of other neurotransmitters known to be present in the adult gut; and 3) examine transiently T-OH-positive cells in cranial sensory ganglia with respect to responsiveness to glucocorticoid hormones.